By using remote plasma atomic layer deposition (ALD), ruthenium thin films were deposited on SiO2 using bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp)2] as a Ru precursor and an ammonia plasma as a reactant. Different plasma treatments were applied, and the best results were obtained with the Ar plasma-treated SiO2 surface. The initial transition region usually observed with Ru deposition before continuous film formation was present, and the number of ALD cycles required to obtain a continuous film was reduced to about 35 cycles on the Ar plasma-treated SiO2 substrates. The transition region of Ru cluster growth on Ar plasma-treated SiO2 was investigated with transmission electron microscopy (TEM). Most of the Ru clusters were larger and better crystallized on the Ar plasma-treated SiO2 than on untreated SiO2. Also, Ru films deposited on the treated SiO2 exhibited a (002) preferred orientated structure with a film resistivity of about 10.26 µΩ-cm. The growth rates of Ru after passing the transition region were similar on both the treated and untreated SiO2 at about 1.7 Å/cycles. From the Auger electron spectroscopy (AES) spectrum, a very low content of oxygen was observed in the Ru films. About 9% carbon was detected by a rutherford backscattering spectrometer (RBS).